1. Field of the Invention
The invention generally relates to a chemical treatment apparatus, especially to a chemical treatment apparatus for wafer production.
2. Description of Related Art
In the semiconductor manufacture, a semiconductor device can be manufactured by multiple processing of wafers. Each processing step affects the yield and performance of the obtained semiconductor device, and therefore it is necessary to severely control the process parameters and operation conditions at each step, especially at etching step which aims at removing off specific sections of the wafer using a chemical solution to form a predetermined structure.
Etching includes two main categories: dry etching and wet etching. The wet etching is implemented by using a chemical apparatus which usually includes an outer bath, an inner bath and a circulation system. The inner bath is located inside the outer bath. The circulation system connects a bottom of the inner bath to a bottom of the outer bath.
The inner bath and the outer bath both contain the chemical solution. The chemical solution flows into the circulation system from the bottom of the outer bath, and then be pressurized by a pump in the circulation system to give the chemical solution energy. Thereafter the chemical solution is heated by a heater at a predetermined temperature, making sure that the etching rate reaches a predetermined value. The chemical solution then flows into the filter to remove out impurities therein. Finally, the chemical solution flows into the inner bath from bottom to top. The above outer bath, the inner bath, the pump, the heater, and the filter connect to each other by a pipe. Since the chemical solution continuously flows into the inner bath, the level of the chemical solution keeps going high. When the level of the chemical solution exceeds an upper edge of the inner bath, the chemical solution overflows into the outer bath. As such, the chemical solution keeps circulation within, in turns, the outer bath and the inner bath.
When the wafer is to be etched, a robot arm picks up at least one wafer from a wafer cassette and places it into the inner bath in a manner that the whole wafer is dipped inside the chemical solution. After a predetermined period of time, the robot arm removes from the inner bath, and the wafer has some sections removed therefore. The wafer material removal rate can be determined by the temperature and the flow speed of the chemical solution. The amount of wafer material removal can be calculated by multiplying the wafer material removal rate with the time of dipping the wafer into the chemical solution.
It is inevitable to have abnormal conditions during etching. If it is the robot arm out of order, then the wafer cannot be timely taken out of the inner bath, causing that the wafer is excessively etched and thus an unexpectable structure is formed. At abnormal conditions, many wafers cannot be used any more and the yield is consequently reduced.
Some approaches have been proposed to deal with such problems. For example, bottoms of the outer bath and the inner bath respectively add a drain valve which is closed when the etching process runs normally. When the robot arm is out of order and the wafer cannot be taken out of the inner bath, the valves are opened to drain out the chemical solution inside the outer and inner baths. Even the wafer stays inside the inner bath, the chemical solution still won't contact the wafer.
Theoretically, the faster the chemical solution drained out, the shorter the period of time the wafer contacts the chemical solution and thus the less the damage to the wafer. The higher percentage of the wafer could be used again based on such an assumption. In fact, the draining of the chemical solution according to the above approach is still not quick enough in terms of percentage of the wafer to be used again.
Consequently, because of the above limitation resulting from the technical design of prior art, the inventor strives via real world experience and academic research to develop the present invention, which can effectively improve the limitations described above.